High-intensity discharge lamps such as super-high pressure discharge lamps may be used as alight source in image display apparatuses such as projectors. In such super-high pressure discharge lamps, the distance between the electrodes for forming an arc increases with use, thereby deteriorating the light efficiency of the optical system, and thus, the illuminance of a display image by an image display apparatus such as a projector is deteriorated. To prevent such deterioration of the illuminance of the display image, it has been proposed to increase a lighting frequency every predetermined period of time in accordance with the rise in lamp voltage in view of the fact that the increase in the distance between the electrodes can be detected based on the rise in the lamp voltage (see, e.g., JP-A-2005-276623). By increasing the lighting frequency, a projection is re-created at the tip of each of the electrodes, thereby preventing the distance between the electrodes from increasing, thus the deterioration of illuminance of the display image can be prevented.
However, depending on the state of the super-high pressure discharge lamp, the lighting frequency is kept at a high level. In this case, so-called arc-jump, in which pluralization of the projections formed at the tip of the electrode associated with deformation or miniaturization of the projections is advanced, and movement of the position where the arc is formed might occur. Further, depending on the lighting frequency kept at a high frequency and the state of the electrodes such as the material or the shape, deterioration such as blackening, in which the electrode material is deposited inside the super-high pressure discharge lamp, might be advanced. Further, when the deterioration of the electrodes is further advanced, it may not be possible to prevent the distance between the electrodes from increasing only by using a constant high lighting frequency, and thus, the illuminance of the display image of the image display device such as a projector might be deteriorated. The same problem exists not only in super-high pressure lamps but also is common in various discharge lamps emitting light caused by arc discharge between the electrodes.